This invention relates in general to resonant fiber optic gyroscopes (RFOGS) and more particularly to a miniature fiber optic resonant gyroscope for mounting as an axial pointing reference on the focal plane substrate within a telescope.
Infrared telescopes are usually cryogenically cooled in order to improve their signal to noise ratio. In order to maintain the telescope optical axis pointed precisely in the desired direction, a pointing reference such as a gyroscope has been employed. However, under cryogenic cooling variations, mechanical dimensions change such that an externally mounted pointing reference may not maintain the optical axis of the telescope pointed in a specific direction. While these differences in direction are small, they can be critical. This problem can be overcome if the pointing reference can be itself mounted within the telescope on the same substrate as the focal plane, or on a suitably located optical element such as a mirror.
Conventional (non-fiber optic) gyroscopes are much too large for this purpose. Interferometric fiber optic gyroscopes (IFOGS) require long lengths of fiber (&gt;200 meters) on a large diameter coil (&gt;3") and so are not well suited as a telescope pointing reference. Resonant fiber optic gyroscopes (RFOGS) require only 10 meters to 100 meters of fiber. Rotation sensitivity is affected by:
1) shot noise that depend on factors such as laser intensity, gyro system loss, laser linewidth, rign resonator linewidth, and photodetector/preamplifier noise; and
2) thermal drift in the presence of polarization crosstalk and optical backscatter.
Because of these factors, RFOGS still require a 3" diameter resonance coil, and so are not well suited for this application.